Control circuit for induction motors



Feb. 10, 1948. w. J. KRUPICK 2,435,25

CONTROL CIRCUIT FOR INDUCTION MOTORS Filed Aug 8, 1946 ATToNEY Patented Feb. 10, 1948 CONTROL cmcm'r ron mnuc'rron MOTORS Walter J. Krupick, Franklin, N. 3., assignor, by

memo assignments, to Kearfott Company, Inc. New York, N. Y., a corporation of New York ,Appllcation August 8, 1948, Serial No. 889,115

4 Claims. (01. 318-207) This invention relates to a motor control circuit and more particularly to a circuit includin a magnetic amplifier for supplying the control winding of a reversible induction motor.

An object of the invention is to provide a control circuit of the above type having novel and improved operating characteristics.

Another object is to provide a circuit of the above type in which the size of the phasing condenser is reduced to a small value as compared to the size required when the condenser is connected directly across the control winding of the induction motor.

Various other objects and advantages will be apparent as the nature of the invention is more fully disclosed.

Although the novel features which are believed to be characteristic of this invention are pointed out more particularly in the claims appended hereto, the nature of the invention will be better understood by referring to the following description, taken in connection with the accompanying drawings forming a part thereof in which a specific embodiment has been set forth for purposes of illustration.

In the drawings:

Fig. 1 is a schematic diagram of a control circuit embodying the present invention; and

lead 4i to a saturating winding 42 of a saturable core transformer 43 having a primary winding 44 and a pair of secondary windings 45 and 48. The return side of the saturating winding 42 is connected by a lead 41 to the lead H on the primary side of the transformer IS. A second anode of the tube 2'! is connected by a lead 5i to a saturating winding 62 of a saturable core transformer 52 having a primary winding 54 and a pair of secondary windings 55 and 58. The return side of the saturating winding 52 is connected by a lead 51 to one side of a secondary 58 of the transformer It, the other side of which is connected by a lead 59 to the supply line i8.

Theprimaries 44 and 54 of the transformers 43 and 53 are connected in series by leads 80, Bi,

82 and 83 across a portion of the secondary 58 betweenva variable tap 84 and the return lead 59. The tap 64 may for example be adjusted to prov'ide 85 volts for the primaries 44 and 54.

The secondaries 45, 55, 48 and 58 are connected in series circuit with a condenser 88 by leads 89 to 15. The secondaries 45 and 55 are connected in series across a control winding 18 of an induction motor 19 by means of leads and BI.

. The induction motor 19 is provided with a fixed Fig. 2 is a schematic diagram of a portion of the circuit in simplified form.

Referring to Fig. 1, a signal of controlled voltage and reversible phase is supplied from the rotor liloi' a variometer ll having a stator l2 supplied by line It from an alternating voltage source such as a 28 volt 400 cycle source. In the embodiment shown this source is derived from a tap l4 on the primary ll of a transformer I! which is supplied by lines I! and it from a suitable voltage source such as 110 volts 400 cycle source.

The rotor i0 is connected by lines 20 to the primary 2| of a transformer 22 having a secondary 23 one side of which is connected by a line 24 to control grids 2B and 28 of a double element tube 21, and the other side of which is connected by a line 28 to the return line It. A condenser 29 is connected across the secondary 22 for controlling the operation thereof. The cathodes 30 and ii of the tube 21 are connected by a common lead 32 to a variable tap 23 of a resistor 34 which is connected across a secondary 25 of the transformer ii. The mid-point 88 of the secondary 2! is connected by a lead 31 to the return line 24.

"One anode 40 of the tube 21 is connected by a phase field winding 82 which is connected across the volt tap 84 on the return side of the secondary 58 by means of leads 83 and 83. The induction motor 19 is provided with a rotor 84 of the squirrel cage type which is caused to rotate in a direction dependent upon the relative phases of'the currents in the windings 18 and 82.

The secondaries II and 58 are connected to oppose the voltages in secondaries 45 and 46, so that when the voltages in the two sets of secondaries are equal no resultant voltage will be applied to the control winding 18 of the motor 18. However, when one of these voltages is increased and the other decreased due to an unbalance in the saturation of the two transformers 43 and 53. the greater voltage will predominate and will be applied to the winding I8 as a control voltage for the motor 19 and will thereby cause the motor to operate in a direction which is dependent upon whether the voltage in the secondaries of the transformer 43 or the volta e in the secondaries of the transformers 52 predominate.

The circuit is arranged so that with a zero signal applied to the grids 25 and equal currents flow in the aths including the saturating windings 42 and 52 and the two transformers 43 and 52 are balanced. thereby supplying no voltage to the control winding ii of the motor It.

quency, but of opposite phase, inasmuch as one {anode is supplied from the secondary B and the i-other from the primary I5 01 the transformer i6,

diflerent space currents will flow in the two space current paths depending upon the relative phasing of the anode voltages and the grid voltages in the two space "'current paths. Hence, an increased current will flow through one of the saturat'in'g windings and a reduced current through the other, thereby unbalancing the operation of the saturable core transformers 63 and 53 and supplying" a control voltage to the winding 18 of the motor 19 which varies in phase according to the phase of the input signal received from the rotor IU of the variometer. This control voltage causes the rotor 84 to rotate in onedirection or the other depending upon the phase relationship between the voltages in the two windings Bland 18.-

In the schematic diagram shown in Fig. 2, the secondaries 45 and 46, 55 and 5B, condenser 63 and winding 18 are shown in simplified form. It will be noted from this diagram that the condenser 68 is connected across all four secondaries, whereas the winding 18 is connected across two opposed secondaries. The condenser fiiiis of a value such that the current in the winding 18 is 90 displaced in phase from the current in the winding 82. purpose were connected directly across the winding 18, a value of several mid. would be required.

.However, by adding a high voltage secondary winding to the saturable core transformer and connecting the condenser across this winding, its capacity is reduced to a small value, such as a few tenths of one mid. The above circuit accordingly reduces the condenser to a practical size and simplifies the operation of the control motor.

It is to be understood of course that the saturable core transformer may be used for other purposes where a voltage of controlled phase is required. Although a specific embodiment of the invention has been shown for purposes of illustration, the invention is not to be restricted thereto, but is only to be limited in accordance wit 7 the scope of the following claims.

What is claimed is;

1. A control circuit for producing an alternat- If a condenser sufiicient for this 4 an output circuit connected across one of said series connected pairs of windings.

2. A control circuit for producing an alternating control voltage of controllable phase, coinprising a pair of saturable core transformers each having a saturating winding, a primary winding and a pair of secondary windings, connection connecting the individual secondary windings of one pair respectively in series opposition with the individual secondary windings of the second pair to form two series connected pairs oi windings, connections connecting the two last pairs in series, a phasing condenser connected across the four series connected windings. and an output circuit connected across oneof said series connected pairs of windings, means including space discharge tubes having a pair of space current paths connected to the respective saturating windings and suppliedby alternating current voltages 180 out of phase and having control grids supplied by an alternating voltage of like frequency, and means varying the relative phase of the grid and space current path voltages for difierentially varying the respective space currents for control purposes.

3. A control circuit for producing an alternating control voltage of controllable phase. comprising a pair of saturable core transformers each having a saturating winding, a primary winding and a pair of secondary windings, connections connecting the individual secondary windings of one pair respectively in series opposition with the individual secondary windings of the second pair to form two series connected pairs of windings, connections connecting the two last pairs in series, a phasing condenser connected across the four series connected windings, and an output circuit connected across one of said series connected pairs of windings, means in cluding space discharge tubes having a pair of space current paths connected to the respective saturating windings and supplied by alternating current voltages 180 out of phase and having control grids supplied by an alternating voltage of like frequency, and means varying the relative phase of the grid and space current path voltages for difierentially varying the respective space current for control purposes, and a reversible induction motor having a control winding connected to said output circuit.

4. A'control circuitfor a reversible induction motor having a. fixed phase winding and a control winding, comprising a pair of saturable core transformers each having a saturating winding, a primary winding and a pair of secondary windings, connections connecting the individual secondary windings of one pair respectively in seing control voltage of controllable phase, comprising a pair ofsaturable core transformers each having a saturating winding, a primary winding and a pair of secondary windings, connections connecting the individual secondary windings of one pair respectively in series opposition with the individual secondary windings of the second pair to form two series connected pairs of windings, connections connecting the two last pairs in series, aphasing condenser connected" across the four seriesv connected windings, and

ries opposition with the individual secondary windings of the second pair to form two series connected pairs of windings, connections connecting the two last pairs in series, a phasing condenser connected across the four eries connected windings, said control winding being connected across one of said series connected pairs of windings.

WALTER J. KRUPICKJ. 

